The objective of the project is to produce a family of radioactive inert indicator substances for use in evaluating alterations of intestinal absorption. The radioactive material will be packaged in an inert insoluble material. The packaged isotope can be produced with a density close to that of solid food (specific gravity 1.2) and particle size ranges from 2 to 100 microns. Studies are under way to determine the influence of particle size on the rate of transit through the bowel. Once the problem in suspending and dispensing the encapsulated isotope are overcome, the material will be used to measure the absorption of radioactive labelled food substances. The insoluble non-absorbable radioactive material act as an indicator substance so that quantitative feeding and stool collection are not necessary.